Our electricity was out last night for about four hours. The clock on our stove this morning showed a time which was about four hours slow (behind the current time), which would be correct.
However, we have two electric alarm clocks, both of which have battery backups and thus both of which should show the correct time this morning. However, both of the clocks are 17 minutes FAST this morning. And I know for a fact that both had the correct time yesterday. So I am gobsmacked. How is this possible? Anyone have a clue?
Are both electric alarm clocks the exact same make and model? This would be more difficult to think of an explanation if they don’t have identical circuits.
The clocks all usually use the line electricity for keeping time. Your clocks with battery backups have to switch to an internal oscillator to keep track of time when the power goes out, and apparently they aren’t very accurate. But it’s better to be 17 minutes early than to have no alarm at all, and miss that big meeting.
For stoves, holding the time constant is a good feature. If you’re away while baking something, and come back to find there was a power failure, you can compare the time, and determine if the food has just been baked a few minutes longer, or if it sat in the cooling oven, breeding bacteria, and needs to be tossed.
I’ve also noticed that my clocks with battery backups run fast. I assume that the 9V battery can’t do as good of a job as 110 VAC at 60 Hrtz.
Plus I’d rather have the alarm go off a few minutes early as opposed to late. If the storm was bad enough, it might take longer to get to work or things might need to be done around the house deal with thawing food in the freezer if power isn’t back on yet.
Both clocks are digital; one is GE and one GTX (?).
I figured it was the difference between battery and 110 but I would have thought the clocks would be slow as first of all a time lapse while changing over and second battery not, as JerrySTL said, doing as good a job. Why would not that add up to clocks being slow rather than fast? If someone could explain that to me I’d be delighted but bear in mind that I don’t totally “get” electricity, if you know what I mean. (I’m a poet not an electrician.) Thanks.
ETA the oven clock didn’t hold the time; it just picked up where it left off and continued from there. Not sure what you meant by “hold the time constant”, ZenBeam. Do you mean, stay where it was? As opposed to the microwave which turned to a blinking “set clock” display and didn’t resume being a clock until I did set it?
My theory, unsupported by specific knowledge, is that when the power ran out both clocks reset to midnight, and then a moment later switched over to internal power and started running again. If the power went out at 11:43 PM, that would be supporting evidence for my theory.
By “hold the time constant”, I meant it remembered the time, but didn’t advance it until power was restored. If the power went out at 3:30, whenever the power came back on, the clock would show 3:30 again, and would start running. (Ours also shows a “PF” for power failure, so you know to check.)
So if the power was out until 4:00, and you looked at the oven clock at 4:45, it would show 4:15, and you’d know it was off for a half hour.
If the power was only off for a minute, when you looked at the oven clock at 4:45, it would show 4:44, and you’d know the time off wouldn’t matter for whatever you were baking.
This is not true: Most clocks use a quarts crystal and its oscillations to keep time. Very few analog clocks and AFAIK no digital clocks use the electrical frequency to gauge time . When it comes to a backup method however, and the child laborer in China, and the last time she suckled is the determining factor on accuracy.
I’d say the test will decide, but I’ve never seen a device that worked that way. You’re postulating a reset and a continuation under battery power from there, an event which I can’t conceive has much practical value. Reset, yes – shows the power was off. Continuing from last known time under battery power – yes, hope springs eternal. Both – serves only to confuse, as the time is always wrong, but you aren’t informed about it.
I had similar issues when working at a remote location in Alaska that had their own power system. The clocks being incorrect was a common problem even without power problems. I would notice clocks being hp to +- 15 minutes off after a couple weeks. We had a lot of brown outs and black outs occured fairly often for a while.
When I asked why my digital alarm clock was off I was told that surges from the power house cause clockes to either run quick or slow.
There was no supporting info and the person I asked had nothing to do with power generation on site.
Well, IMO it shouldn’t work that way, because if the backup power is supposed to keep the clock accurate, this would be a terrible way to do it. But it’s all I could think of that might fit the known facts.
If you had to set the time again to use the battery backup, that would make the battery backup utterly useless. The whole point of the battery is so that you don’t lose the time.
We need to define things more narrowly here. Not all clocks work the same way. I have a digital-display clock that’s 30 years old, and I’m pretty sure it syncs to the line frequency. Do the new ones work that way? I’m not sure.
I do know they used to, since the power companies were very careful to be accurate so they could exchange power.
I once lived in a remote area that was supplied by an old diesel generator. The operator claimed that if he ran the output at 60hz, it would fly apart, so he kept it somewhere in the 40-50hz range. As a result, all our clocks ran slow, our movie projectors ran slow, and our refrigerators weren’t too happy, either.
Or, the backup batteries had failed in both clocks. The electricity was off for four hours, but came back ON at 11:43, at which point the clocks started running again, from 12:00.
